Double wall combustor tile arrangement

ABSTRACT

A double wall structure ( 22 ) for a combustor ( 15 ) of a gas turbine engine ( 10 ) comprising an inner wall ( 28 ) and an outer wall ( 27 ), the inner wall ( 28 ) comprising a plurality of main tiles ( 50 ), the main tiles ( 50 ) are secured to the outer wall ( 27 ) by a securing means ( 35 ), wherein the inner wall ( 28 ) further comprises a plurality of edge tiles ( 52 ) which are secured to the outer wall ( 27 ) by securing means ( 35 ), each edge tile ( 52 ) overlapping at least one edge ( 30, 31, 54, 61 ) of a main tile ( 50 ) thereby further securing the main tiles ( 50 ) to the outer wall ( 27 ).

[0001] This invention relates to improvements to a combustor of a gasturbine engine and in particular to an arrangement of heat resistanttiles of a double wall of a combustor.

[0002] In a double walled combustor of a gas turbine engine it is knownto provide an inner wall which comprises heat resistant tiles withpedestals, which extend toward the outer wall thereby improving heatremoval by a cooling air flow between the walls. The tiles are securedto the outer wall by integral studs, which are intended to allow thetiles to expand and contract with the thermal cycle of the engine.However, it is known that the studs lock-up and prevent thermal movementof the tiles. This damages the tiles and leads to large gaps around thetiles and an undesirable increase in the amount of cooling air required.

[0003] One way of reducing combustion product emissions is to employlean-burn combustion which limits the peak flame temperature and henceproduction of nitrides of oxygen (NOx). To achieve lean-burn most of acompressed air flow from a compressor of the engine has to be committedto fuel/air mixing modules, with little compressed air remaining forcooling the combustor walls.

[0004] Employing the most advanced double wall cooling designs possiblefor lean-burn combustors is hence very beneficial to NOx control tominimise the cooling air quantity required. This enables the fuel/airmixing modules to be run even leaner and hence further reduces NOxemissions.

[0005] It is therefore an object of the present invention to provide acombustor double wall arrangement, which minimises the amount of coolingfluid used and allows tiles to expand and contract with the thermalcycle of the engine.

[0006] According to the present invention a double wall structure for acombustor of a gas turbine engine comprising an inner wall and an outerwall, the inner wall comprising a plurality of main tiles, the maintiles are secured to the outer wall by a securing means, wherein theinner wall further comprises a plurality of edge tiles which are securedto the outer wall by securing means, each edge tile overlapping at leastone edge of a main tile thereby further securing the main tiles to theouter wall.

[0007] Preferably, the edge of the main tile comprises a stepped edgehaving a leg portion extending from the main tile towards the outer walland a foot portion extending from a distal end of the leg portion, theedge is arranged to space apart the main tile from the outer wall, thefoot portion being in slideable contact with the outer wall and theoverlapping edge tile.

[0008] Alternatively, the edge of the main tile comprises a leg portionextending from the main tile towards the outer wall, the edge isarranged to space apart the main tile from the outer wall, the legportion having a distal end in slideable contact with the outer wall,the overlapping edge tile being in slideable contact with the edge.

[0009] Preferably, the securing means is a stud, the stud comprises athreaded plug and a nut, in use the threaded plug is secured to the tileand extends through a hole defined in the outer wall and onto which thenut is fastened.

[0010] Preferably, the threaded plug of the stud further comprises athickened portion, the thickened portion is disposed between the tileand the outer wall and defines the space therebetween.

[0011] Preferably, the edge tile overlaps adjacent edges of adjacentmain tiles, the edges being generally aligned with a principal axis ofthe engine.

[0012] Preferably, the edge tile overlaps adjacent edges of adjacentmain tiles, the edges being generally circumferentially aligned withrespect to a principal axis of the engine.

[0013] Preferably, the edge tile overlaps adjacent edges of adjacentmain tiles, the edges being generally axially aligned with a principalaxis of the engine and the edges being generally circumferentiallyaligned to the principal axis.

[0014] Preferably, the edge tile comprises a plurality of angledeffusion cooling holes.

[0015] Alternatively, the edge tile comprises a plurality of pedestals,each pedestal extending from the edge tile toward the outer wall.

[0016] Preferably, the securing means is located generally centrally ofthe main tiles. Preferably, the securing means is tightly secured to themain tiles. Preferably, further securing means are provided, the furthersecuring means are loosely secured to the main tiles.

[0017] Preferably, a gas turbine engine comprising a combustor whereinthe combustor comprises a double wall structure as hereinbeforedescribed.

[0018] Preferably, a method of assembling a double wall structure of acombustor of a gas turbine engine, the wall structure comprising anouter wall and an inner wall, the method comprising the steps of:securing a plurality of main tiles to the outer wall by a first securingmeans; securing a plurality of edge tiles to the outer wall by securingmeans so that each edge tile overlaps at least one edge of a main tilethereby further securing the main tile to the outer wall.

[0019] Embodiments of the invention will now be described by way ofexample only, with reference to the accompanying diagrammatic drawings,in which:

[0020]FIG. 1 is a sectional side view of a gas turbine engineincorporating a combustor in accordance with the present invention.

[0021]FIG. 2 shows a sectional side view of part of a combustor of theengine shown in FIG. 1;

[0022]FIG. 3 shows a prior art sectional side view of a part of aradially outer wall structure of a combustor showing a wall element;

[0023]FIG. 4 is a sectional side view A-A on FIG. 2 showing part of aradially outer wall structure of a combustor double wall element of afirst embodiment of the present invention;

[0024]FIG. 5 is a sectional side view A-A on FIG. 2 showing part of aradially outer wall of a combustor double wall element of a secondembodiment of the present invention.

[0025] With reference to FIG. 1, a ducted fan gas turbine enginegenerally indicated at 10 has a principal axis X-X. The engine 10comprises, in axial flow series, an air intake 11, a propulsive fan 12,an intermediate pressure compressor 13, a high-pressure compressor 14,combustion equipment 15, a high-pressure turbine 16, an intermediatepressure turbine 17, a low-pressure turbine 18 and an exhaust nozzle 19.

[0026] The gas turbine engine 10 works in the conventional manner sothat air entering the intake 11 is accelerated by the fan 12 to producetwo air flows, a first air flow into the intermediate pressurecompressor 13 and a second air flow which provides propulsive thrust.The intermediate pressure compressor 13 compresses the airflow directedinto it before delivering that air to the high-pressure compressor 14where further compression takes place.

[0027] The compressed air exhausted from the high-pressure compressor 14is directed into the combustion equipment 15 where it is mixed with fueland the mixture combusted. The resultant hot combustion products thenexpand through, and thereby drive, the high, intermediate andlow-pressure turbine 16, 17 and 18 before being exhausted through thenozzle 19 to provide additional propulsive thrust. The high,intermediate and low-pressure turbines 16, 17 and 18 respectively drivethe high and intermediate pressure compressors 14 and 13 and the fan 12by suitable interconnecting shafts (not referenced).

[0028] Referring to FIG. 2, the combustor 15 is constituted by anannular combustion chamber 20 having radially inner and outer wallstructures 21 and 22 respectively. The combustor 15 is secured to a wall23 by a plurality of pins 24 (only one of which is shown). Fuel isdirected into the chamber 20 through a number of fuel nozzles 25 locatedat an upstream end 26 of the chamber 20. The fuel nozzles 25 arecircumferentially spaced around the engine 10 and serve to spray fuelinto air derived from the high-pressure compressor 14. The resultantfuel/air mixture is then combusted within the chamber 20.

[0029] The combustion process takes place within the chamber 20 andnaturally generates a large amount of heat. It is necessary therefore,to arrange that the inner and outer wall structures 21 and 22 arecapable of withstanding the heat.

[0030] The radially inner and outer wall structures 21 and 22 eachcomprise an outer wall 27 and an inner wall 28. The inner wall 28 ismade up of a plurality of discrete wall elements in the form of tiles29A and 29B.

[0031] Each of the tiles 29A, 29B has circumferentially extending edges30 and 31, and the tiles are positioned adjacent each other, such thatthe edges 30 and 31 of adjacent tiles 29A, 29B overlap each other.Alternatively, the edges 30, 31 of adjacent tiles can abut each other.Each tile 29A, 29B comprises a base portion 32 which is spaced from theouter wall 27 to define therebetween a space 44 (see FIG. 3) for theflow of cooling fluid in the form of cooling air as will be explainedbelow. Heat removal features in the form of pedestals 45 (see FIG. 3)are provided on the base portion 32 and extend into the space 44 towardsthe outer wall 27.

[0032] Conventionally, and as shown in the arrangement of FIG. 2,(first) securing means (35) are in the form of studs 35 comprisingthreaded plugs 34 and nuts 36. Each tile 28 has a plurality of threadedplugs 34 extending from the base portions 32 of the tiles 29A, 29Bthrough apertures in the outer wall 27. Nuts 36 are screwed onto theplugs 34 to secure the tiles 29A, 29B to the outer wall 27.

[0033] Referring to FIG. 3, during engine operation, some of the airexhausted from the high-pressure compressor 14 is permitted to flow overthe exterior surfaces of the chamber 20. The air provides the chamber 20with cooling with some of this air being directed into the interior ofthe chamber 20 to assist in the combustion process. First and secondrows of mixing ports 38, 39 are provided in the tiles 29B and areaxially spaced from each other. The ports 38 correspond to apertures 40in the outer wall 27, and the ports 39 correspond to apertures 41 in theouter wall 27.

[0034] Referring particularly to the tiles 29B, arrow A in FIG. 3indicates air exiting via the open upstream edge 30 of the tile 29B andmixing with downstream air flowing from the upstream adjacent tile 29A,as indicated by arrow B. Arrow C indicates the resultant flow of air.Angled effusion holes 46 are provided centrally of the tile 29B betweenthe ports 38 and 39. Arrow D indicates a flow of air exiting from thespace 44 through the effusion cooling holes 46. Also, a flow ofdownstream air exits from the open downstream edge 31 of the tile 29Bafter mixing with upstream air flowing from the adjacent tile 29A, asindicated by arrow E. Air flows indicated by arrows C and E provide afilm of cooling air over the interior surface of the tiles 29A and 29Bthereby preventing overheating caused by the combustion of gases in thechamber 20.

[0035] During a normal operation cycle of the engine 10 the combustor 20will be subject to varying amounts of combustion heat. This causes thetiles 29A and 29B to thermally expand relative to the outer wall 27. Thestuds 35 which allow the tiles 29A and 29B to slide usually accommodatethese thermal expansions. However, it is known that some of the studs 35prevent the tiles 29A and 29B from sliding particularly at extremeengine 10 operating conditions. This leads to high stresses in the tile29A, 29B at elevated temperatures and subsequently premature failurethereof. Furthermore, if the nuts 36 are overtightened the tiles 29A,29B will lock-up against the studs 35 as they thermally expand causingdistortion, leading to fatigue and cracking. If the nuts 36 are loosethen both frettage and cooling flow leakage around the tiles 29A, 29Bedges 30, 31 will occur. These problems are more severe where advancedhigh-temperature alloys are used for the tiles 29A, 29B, because,although the alloys have superior oxidation properties they haveinferior strength, when compared to conventional tile material.

[0036] To obviate these problems it would be easy to think that onesolution would be to use a central stud 35 in each tile 29A, 29B therebyallowing the tile to be unconstrained at the (circumferential) edges 30,31, as well as axially aligned edges (54, 61 in FIG. 4). However, it islikely that there would be significant and uncontrolled cooling fluidleakage around the (circumferential) edges 30, 31 and 54, 61 in FIG. 4,which in turn would lead to a reduced amount of coolant flow through theeffusion cooling holes 46 and subsequent over-heating of the tiles 29A,29B. An additional concern is that should the stud 35 fail the wholetile 29A, 29B would be released into the combustor 15 and passesdownstream into the high-pressure turbine 16.

[0037] Referring now to FIG. 4, the outer wall structure 22 comprisesthe inner wall 28 arranged in accordance with a first embodiment of thepresent invention. The inner wall 28 comprises main tiles 50 and edgetiles 52. The main tiles 50 are bolted to the outer wall 27 by agenerally centrally located stud 35. The stud 35 is similar to thathereinbefore referred to and in use the threaded plug 34 is castintegrally with the tile 50, 52 and extends through a hole 33 defined inthe outer wall 27 and onto which the nut 36 is fastened. Alternatively,the threaded plug 34 may be brazed to the tile 50, 52. This generallycentrally located stud 35 tightly secures the main tile 50, as there islittle or no relative movement at the centre of the tile 50.

[0038] Main tiles 50 are generally similar to the tiles 29A, 29B havingpedestals 45 and effusion cooling holes 46, however, the tiles 50further comprise stepped edges 54. The stepped edge 54 comprises a legportion 58 and a foot portion 56. The leg portion 58 extends from themain tile 50 towards the outer wall 27 and at its distal end 55 the footportion 56 extends away from and in generally the same plane as the maintile 50. The foot portion 56 is arranged to seal against the outer wall27 and is in slideable contact therewith.

[0039] Where two circumferentially adjacent tiles 50 meet, an edge tile52 is positioned to overlap the foot portion 58 of each adjacent tile50. It is preferable for the edge tile 52 to be in slideable contactwith the main tiles 50 so that the main tiles 29A, 29B are able tothermally expand and contract in their main plane. However, a smallclearance may be provided between the foot portion 56 and both the outerwall 27 and the edge tile 52.

[0040] An expansion gap 48 is defined between the main tile 50 and theedge tile 52 to accommodate the thermal expansion of the main tile 50.Similarly, a second expansion gap 47 is defined between the stud 35 andthe foot portion 56 to accommodate the thermal expansions.

[0041] A stud 35 has its threaded plug 34 cast integrally with the edgetile 52 and is secured by the nut 36 in conventional manner to the outerwall 27. The edge tile 52 may be provided with more than one stud 35along its axial length. The outer wall 27 is provided with apertures 60(not shown where the edge tile is) to allow cooling fluid into the space44 between the tiles 52, 50 and the outer wall 27.

[0042] In addition, the edge tiles 52 represent only a small fraction ofthe total wall 22 area so a relatively large amount of cooling air maybe used, compared to that supplied to the larger main tiles 29A, 29B.The edge tiles 52 can hence be operated at relatively cool temperatures,enabling minimal distortion thereof, therefore providing good locationand slideable sealing engagement with the main tiles 29A, 29B. Thereforethe edge tiles 52 may be made of a lower temperature capable and lowercost material than the larger main tiles 29A, 29B.

[0043] A further improvement of the arrangement of the present inventionis the ease of assembly. The large main tiles 50 are assembled to thecombustor outer wall 27 when cold and secured by their central stud 35fixing, followed by fitting of the edge tiles 52. The conventionalalternative approach of using edge-sealing strips (not shown, butcommonly known in the art) that slide into slots on the tile edgespresent considerable assembly problems and even greater dismantlingproblems after service.

[0044] Importantly, should the main tile's 50 centre stud 35 fail, thetile 50 will remain secured to the outer wall 27 by the edge tiles andso cannot be released into the combustor 15. For safety reasons it maystill be prudent to provide additional studs 35 near to the edges 30,31, 54, 61 of the main tile 50, however these additional studs 35 wouldbe relatively loosely fitted so as to not restrain the thermal growth ofthe main tiles 50.

[0045] Referring now to FIG. 5, a second embodiment of the presentinvention relates to the arrangement of the main tile 50 edges and theedge tile 52. The main tile 50 comprises an edge 61 and the leg portion58, the leg portion 58 extending from the edge 61 toward the outer wall27. The distal end of the leg portion is in slideable contact with theouter wall 27. The edge tile 52 is arranged to overlap the edges 61 oftwo adjacent main tiles 50, thereby securing the main tiles 50 to theouter wall 27. The edge tile 52 comprises a rim 64, which is inslideable contact with edges 61. The rim 64 comprises cooling holes 65.The threaded plug 34 further comprises a thickened portion 62 arrangedto space apart the edge tile 52 and the outer wall 27.

[0046] It should be apparent to one skilled in the art that not only maythe edge tiles 52 secure the main tiles 50 along their generally axiallyaligned edges 54, 61, but may also secure the main tiles 50 along theircircumferential edges 30, 31.

[0047] Although the main tiles 50 have been described with reference tohaving pedestals 45, impingement cooling may alternatively cool thetiles 50. A configuration of an impingement-cooling tile (or wallelement) is described and incorporated herein with reference to EuropeanPatent EP0576435 of the present Applicant. The edges of the wallelements described in EP0576435 are intended to be of a similarconfiguration as described herein. Furthermore and in accordance withthe present invention the inner wall of EP0576435 is provided with edgetiles.

[0048] Whilst endeavouring in the foregoing specification to drawattention to those features of the invention believed to be ofparticular importance it should be understood that the Applicant claimsprotection in respect of any patentable feature or combination offeatures hereinbefore referred to and/or shown in the drawings whetheror not particular emphasis has been placed thereon.

We claim:
 1. A double wall structure for a combustor of a gas turbineengine comprising an inner wall and an outer wall, the inner wallcomprising a plurality of main tiles, the main tiles are secured to theouter wall by a securing means, wherein the inner wall further comprisesa plurality of edge tiles which are secured to the outer wall bysecuring means, each edge tile overlapping at least one edge of a maintile thereby further securing the main tiles to the outer wall.
 2. Adouble wall structure as claimed in claim 1 wherein the edge of the maintile comprises a stepped edge having a leg portion extending from themain tile towards the outer wall and a foot portion extending from adistal end of the leg portion, the edge is arranged to space apart themain tile from the outer wall, the foot portion being in slideablecontact with the outer wall and the overlapping edge tile.
 3. A doublewall structure as claimed in claim 1 wherein the edge of the main tilecomprises a leg portion extending from the main tile towards the outerwall, the edge is arranged to space apart the main tile from the outerwall, the leg portion having a distal end in slideable contact with theouter wall, the overlapping edge tile being in slideable contact withthe edge.
 4. A double wall structure as claimed in claim 1 wherein thesecuring means is a stud, the stud comprises a threaded plug and a nut,in use the threaded plug is secured to the tile and extends through ahole defined in the outer wall and onto which the nut is fastened.
 5. Adouble wall structure as claimed in claim 4 wherein the threaded plug ofthe stud further comprises a thickened portion, the thickened portion isdisposed between the tile and the outer wall and defines the spacetherebetween.
 6. A double wall structure as claimed in claim 1 whereinthe edge tile overlaps adjacent edges of adjacent main tiles, the edgesbeing generally aligned with a principal axis of the engine.
 7. A doublewall structure as claimed in claim 1 wherein the edge tile overlapsadjacent edges of adjacent main tiles, the edges being generallycircumferentially aligned with respect to a principal axis of theengine.
 8. A double wall structure as claimed in claim 1 wherein theedge tile overlaps adjacent edges of adjacent main tiles, the edgesbeing generally axially aligned with a principal axis of the engine andthe edges being generally circumferentially aligned to the principalaxis.
 9. A double wall structure as claimed in claim 1 wherein the edgetile comprises a plurality of angled effusion cooling holes.
 10. Adouble wall structure as claimed in claim 1 wherein the edge tilecomprises a plurality of pedestals, each pedestal extending from theedge tile toward the outer wall.
 11. A double wall structure as claimedin claim 1 wherein the securing means is located generally centrally ofthe main tiles.
 12. A double wall structure as claimed in claim 1wherein the securing means is tightly secured to the main tiles.
 13. Adouble wall structure as claimed in any one of claims 1-12 whereinfurther securing means are provided, the further securing means areloosely secured to the main tiles.
 13. A gas turbine engine comprising acombustor wherein the combustor comprises a double wall structure asclaimed in claim
 1. 14. A method of assembling a double wall structureof a combustor of a gas turbine engine, the wall structure comprising anouter wall and an inner wall, the method comprising the steps of:securing a plurality of main tiles to the outer wall by a securingmeans; securing a plurality of edge tiles to the outer wall by securingmeans so that each edge tile overlaps at least one edge of a main tilethereby further securing the main tile to the outer wall.